A gummy musket is when a person who chews a lot of gum (Nicorette,Dentine,etc) routinely swallows it rather than spit it out when spent. Subsequent bowel movements often result in the gum getting matted in the ass hair as a result of wiping. Removal of embedded gum is difficult and painful.

I jerked out a gigantic tuft of ass hair on account of a gummy musket.